1. Field of the Invention
This invention relates to an optical rotary encoder capable of detecting rotating angles of a rotating body to be measured by use of a light emitting diode and light receiving elements, and more particularly to an optical rotary encoder of a light reflecting type.
2. Description of Prior Art:
Optical rotary encoders of light reflecting type and light transmitting type have been widely known. FIG. 1 illustrates a light reflecting type rotary encoder, and FIG. 2 illustrates, in much enlarged scale, a detecting portion of the light reflecting type rotary encoder shown in FIG. 1. As shown in the drawing, the conventional rotary encoder comprises a rotatable disc 1, the rotating angle of which is to be measured. A number of reflecting portions 2 are provided on the surface of the rotatable disc 1 at a predetermined pitch, while the same number of non-reflecting portions 3 are provided between the reflecting portions 2 in an interposed manner. The rotatable disc 1 is secured to a rotating shaft (not shown) to be rotated therewith.
A supporting member 4 with two mounting holes 5 and 6 is provided adjacent to a peripheral portion of the disc 1 in a relation opposing thereto. A light emitting element such as a light emitting diode (LED) 7 is mounted in the hole 5, while a light receiving element 8 such as a phototransistor is mounted in the hole 6. When one of the reflecting portions 2 of the disc 1 is brought into opposition to the holes 5 and 6 provided through the supporting member 4, light emitted from the light emitting diode 7 is reflected by the reflecting portion 2 to be received in the light receiving element 8 which delivers an output signal of high level. Conversely, when the holes 5 and 6 are brought into opposition to one of the nonreflecting portions 3, the light emitted from the light emitting diode 7 is absorbed by the nonreflecting portion 3, rendering the output signal from the light receiving element 8 to be low level. As a consequence, a pulse signal is delivered from the light receiving element 8 according to the rotation of the rotating disc 1, and by counting the number of the pulses of the pulse signal, a rotating angle of the rotating disc 1 can be detected.
The above described light emitting diode 7 used as a light source in the optical rotary encoder, however, reduces its light emitting property when the temperature thereof becomes high, and therefore the intensity of the pulse signal delivered from the light receiving element 8 is varied in accordance with the temperature variation. Such a result entails a serious difficulty when a high precision detection of the rotating angle of the rotating disc 1 is required.